PS6-17. Association Between Estrous Expression Behavior Detected by an Ear-tag Activity Sensor and Fertility Outcomes in Angus Beef Cows.

Abstract The objective of this study was to evaluate the association between estrous expression and fertility outcomes, and to assess the agreement between a breeding indicator (Estrotect, Rockway, Inc., Spring Valley, WI) and an ear-tag activity sensor (CowManager, Harmelen, Netherlands) for estrus detection in Angus beef cattle. Data from 89 Angus beef cows were evaluated, including estrus alert characteristics (intensity and duration), breeding indicator score at AI, cow temperament score at calving, and days postpartum at AI. Cows were synchronized using 7-day CO-Synch+CIDR® and Split-TAI. Estrus intensity was quantified using the maximum activity value generated at alert by the ear-tag activity sensor (unit: index). Blood samples were collected on d 17, 24, 28, and 35 post-AI to measure concentrations of pregnancy-specific protein B (PSPB). Each cow's individual baseline PSPB concentration was determined, and cows were classified as pregnant when PSPB increased by at least 12.5% from d 17 to d 24. Early embryonic loss was defined as a relative decrease in PSPB concentration between d 24 and d 35 post-AI. Data were analyzed using linear mixed models and logistic regression analyses, and cow was the experimental unit. Agreement between the breeding indicator patch and the ear-tag activity sensor alerts was evaluated by classifying each into three levels. Breeding indicator scores were classified as no, low, or high activation, whereas activity alerts were classified as no alert (< 5), low (5-8), or high (>8). Agreement was assessed using sensitivity, specificity, overall agreement, and Cohen's kappa coefficient. A total of 94.4% of animals were inseminated during estrus, whereas 5.6% were inseminated following the timed AI protocol. Only animals inseminated during estrus (n = 84) were included in the final analysis. Overall pregnancy per AI was 52.9%, and early embryonic loss occurred in 15.4% of pregnancies. Greater estrus intensity (odds ratio (OR) = 1.28; P= 0.018) and longer estrus duration (OR = 1.05; P= 0.041) were positively associated with the occurrence of pregnancy. Days postpartum at AI (P = 0.31) and cow temperament score at calving (P = 0.40) were not associated with pregnancy outcome. Cows maintaining pregnancy exhibited greater estrus intensity compared with cows experiencing early embryonic loss (9.6 vs 7.1; P= 0.047). There was agreement between the estrus detection methods, with sensitivity of 0.83, specificity of 0.78, and a Cohen's kappa coefficient of 0.61. These findings indicate that stronger estrous expression and longer estrus duration are associated with improved fertility and reduced risk of early embryonic loss in beef cows. Additionally, the automated activity monitoring system showed high agreement with breeding indicators and may serve as complementary estrus detection tools.